1. Field of the Invention
The object of the invention is an ovenable food tray consisting of a board base of paperboard or cardboard provided with at least one heat resistant polymeric coating layer. Another object of the invention is a manufacturing method of such a food tray.
2. Description of Related Art
Ovenable food trays, such as microwave oven or conventional oven trays, are used as parts of consumer packages of foodstuffs, such as casserole foods intended to be heated, and they are also sold as separate products. Such underlayers must be impermeable to water and grease; and in addition to this, sufficient heat-resistance is required from ovenable trays. Up till now, polyester-coated paperboard has been used in ovenable trays. Its disadvantages include the thickness of the required polymeric layer and the fact that it is very difficult for the polymeric coating to withstand typical oven temperatures of more than 200.degree. C. The microwave oven trays intended to be heated in microwave ovens have been provided with a polymeric coating of polypropylene but its heat-resistance is also limited.
In the EP application 0 245 005 there is described an ovenable food tray which consists of a laminate of paper and paperboard layers and has a coating of a food grade resin such as polyethylene terephtalate (PET) on its food contacting side and a nonburning coating of silicone polymer on the reverse side, covering the paper layer of the laminate. While the silicone coating possesses an increased resistance to heat the use of polyethylene terephtalate still limits the ability of the tray to withstand high oven temperatures.